TC-50 Early / Late Model Differences
In 1988 Spica offered an upgrade to existing owners and all new units after this date (post 7500 serial numbers) were built to this spec. I have seen these newer units referred to as TC-50i and TC-50II, tweeters, woofers and crossovers changed with this upgrade.
Can you tell from the outside which model you have?
Early TC-50 units have a rectangle hole in the felt surrounding the tweeter, later units (TC-50i), have a small square hole. When in doubt check the actual driver manufacturer’s part numbers stamped on the drivers.
If you are replacing only one woofer, you can do this reliably by matching the service code and part number on the driver. If you are unable to locate matching service codes you can replace the drivers from a set off eBay, as long as you swap the the woofers and crossovers to maintain matching. If you are swapping late for early or vise versa, just remember that the woofers, tweeters, and crossovers were changed with the upgrade.
| Drivers Used in TC-50s: | |||
| Dates | Serial Numbers | Woofers | Tweeters |
| Before 1988 | pre-7500 | HIF 17JS 2 CA12 (specs*) | HD 100 D25 (specs*) |
| After 1988* | after 7500 (or upgraded) | HIF 17JVX 2CA 2 | DTW 100 TF |
Except for the SC-50 and TC-60 all Spica original drivers were manufactured by Audax of France and labeled Polydax in the US. Audax no longer manufactures replacement woofers. *The specs listed here are correct for response curves etc, but are for the 8 ohm version of the drivers used in the TC-50, however Spica used the 4 ohm versions of these units.
Rebuilding \ Repairing Speaker Drivers
The voice coil of woofers and tweeters can be rewound by a competent speaker rebuilder. However, if you have a physically damaged cone or rubber surround (Cats!) you may be out of luck. Everyone I have contacted so far says the butyl surrounds for the woofers are no where to be found. This means a rebuilder will use foam surrounds. Foam surrounds will significantly alter the mass of the woofer and its sound.
Replacement Drivers
The original drivers were manufactured by Audax (FR) / Polydax (US). Audax no longer manufactures replacement woofers. If you could find Spica graded new old stock (NOS) with the proper service codes that would be ideal, perhaps just as good would be to cannibalize a used set. Other options would be non-graded, NOS Audax (FR) / Polydax (US) replacement, which turn up on eBay from time to time, or getting your driver rewound by a rebuilder. If you go the rebuilder route, I could see a strong case to have your drivers redone in pairs.
Madisound offers the Audax 4 ohm TW025A2 driver (specs) as a replacement tweeter. On inspection (based on the length of the voice coil), these appear to be a match for the earlier the HD 100 D25 tweeters. You should note that the terminals on the TW025A2 tweeters are located about 20 or 30 degrees apart (if the speaker were the face of a clock the terminals would be at 5 and 7 o'clock). The terminals on the original units are located 180 degrees apart (using the clock again, the terminals were at 3 and 9 o'clock), so some cabinet modification will be necessary.
What if the service codes for the woofers don't match?
I don't want to be too crazy here, if your choice is a working Spica versus the dumpster, you should be open to some compromises. Early on I had a problem with my pre-amp. It would occasionally burp DC and fry a woofer. The replacements from Spica were around $80, plus the time and cost to ship. I found a local source for a generic Polydax woofer ($25) and replaced one side with the non-doped version. While the precise imaging could not have been as good as a matched units, the crossovers would still be time aligned and volume matched over much of the audio range.
Speaker Cone Doping
The woofers of the TC-50 and 50i were doped in a mix of Elmer's glue and water. According to the (SLUG Post 836), the Elmer's glue is mixed 60:40 glue to water (3:2). They first placed an 1/8" bead is put around the base of the cone and let it dry, then cone is coated. It is believed that the TC-50s had one coat, while TC-50i's had two coats (SLUG post 160).